This invention relates to olefin polymerization processes for polymerizing ethylene, higher alpha-olefin comonomer and dienes, especially vinyl norbornene, and especially processes for producing amorphous or semi-crystalline polymers such as EPDM. The invention also relates to the novel polymers produced by such processes. The invention furthermore relates to articles of manufacture with an improved balance of toughness and curing properties.
EPDM""s containing vinyl norbornene (VNB), which is a non-conjugated diene having two polymerizable double bonds, are known from EP843698; EP843702 and EP843701. These polymers have long chain branching (LCB). High levels of LCB improve processability, but may impair physical properties (tear) of final product after conversion of the polymer by extrusion or molding etc. The two double bonds are both capable of polymerization with olefins in the presence of transition metal catalysts.
The prior art describes the benefit of VNB over ethylidene norbornene (ENB). ENB is a non-conjugated diene having one double bond that is copolymerizable using a transition metal catalyst. The other double bond is not so polymerizable and remains available in the final polymer for subsequent reaction, e.g., sulfur curing. The VNB derived EPDM provides improved cure rate and performance in free-radical curing, improved processability from the highly branched structure and requires a low level of diene to provide suitable physical properties in the final product comparable to ENB derived EPDM.
WO99/00434 describes combining ENB, VNB and specific branching inhibitors to produce EPDM with reduced branching. The ENB derived units are present in amounts well in excess of the amount of VNB. The spectrum of LCB and MWD variations that can be obtained appear to be limited by the process characteristics (a branching modifier is used). Very low levels of branching may be hard to obtain because of cationic branching generated by the ENB. Broad molecular weight distribution is favored.
In the present invention, an alternative method is used for controlling LCB, which permits greater reliance on the non-conjugated diene type which has two polymerizable double bonds, such as VNB. In this alternative method no, or much less, ENB can be used. Thus the benefits described for prior art EPDM polymers derived predominantly from VNB as the diene can be obtained, with the added benefit of balancing the influence of LCB on processing and the properties of the final product.
This method relies not on chemical branching modifiers, but on the predominant addition of the VNB (or equivalent diene having two polymerizable double bonds) in a second polymerization reaction step under polymerization conditions which allow for controlled incorporation of the VNB.
It is known to make EPDM type polyolefins, generally those having ENB derived units, in a continuous stirred tank series reactor layout, primarily to obtain broader molecular weight distributions and the attendant processability benefits resulting therefrom. Reference is made to U.S. Pat. No. 4,306,041; EP227206 and WO99/45047; WO99/45062 discusses polymer dispersions. The production of an EPDM product containing predominantly units of VNB for the diene so as to control levels of LCB is not described.
U.S. Pat. No. 6,319,998 and WO 99/45062 describe processes using metallocene type catalysts that have high activity and extremely efficient incorporation of diene. This leads to high levels of LCB, and in some cases the formation of gel. The process described herein employs a catalyst capable of controlling VNB incorporation so as to limit LCB formation.
For additional background see: WO 99/00434, U.S. Pat. No. 6,207,756, WO 98/02471, U.S. Pat. No. 3,674,754, U.S. Pat. No. 4,510,303U.S. Pat. No. 3,629,212, U.S. Pat. No. 4,016,342, U.S. Pat. No. 5,674,613, EP 1088855, U.S. Pat. No. 6,281,316, EP 784062, U.S. Pat. No. 4,510,303, U.S. Pat. No. 5,698,651 and U.S. Pat. No. 6,225,426.
The present invention relates to a process for solution polymerizing ethylene, higher alpha-olefin and diene having two polymerizable double bonds which comprises: A) reacting in a first step ethylene, higher alpha-olefin comonomer and optionally one or more dienes to produce a polymer composition comprising from 0 to less than 1 mol % of diene having one or two polymerizable double bonds, in the presence of a catalyst system;
reacting in a second step ethylene, higher alpha-olefin comonomer and one or more dienes at least one of which is a diene having two polymerizable double bonds in the presence of a catalyst system, the amount of diene having two polymerizable double bonds being added to the reactor in the second step being more than 50% of the total diene added in the first and second step combined; and C) recovering a polymer product having from 0.02 to 2 mol % of units derived from the diene having two polymerizable double bonds, and a branching index of greater than 0.5.
In one embodiment, the present invention relates to a process for solution polymerizing ethylene, propylene and diene having two polymerizable double bonds which comprises: A) reacting in a first step ethylene, propylene and optionally one or more dienes to produce a polymer composition comprising from 0 to less than 1 mol % of diene having one or two polymerizable double bonds, in the presence of a vanadium based catalyst system; B) reacting in a second step ethylene, higher alpha-olefin comonomer and diene comprising vinyl norbornene in the presence of the same catalyst system, the amount of vinyl norbornene added in the second step being more than 50% of the total diene added in the first and second step combined; and C) recovering a polymer product having from 0.1 to 1 mol % of units derived from vinyl norbornene and a total of no more than 5 mol % diene derived units, from 50 mol % to 90 mol % ethylene derived units and a balance of propylene derived units; a branching index of greater than 0.5, preferably greater than 0.7 and a Mooney viscosity of from 15ML to 100 MST.
This invention further relates to a polymer product which comprises in combination: a) from 50 to 90 mol % of ethylene derived units ; b) from 0.1 to 2 mol % of VNB derived units; c) an optional amount of ENB derived units; d) a balance of higher alpha olefin derived units; and e) a branching index of greater than 0.5.
More specifically this invention relates to a polymer product which comprises in combination: a) from 50 to 90 mol % of ethylene derived units; b) from 0.1 to 1 mol % of VNB derived units; c) an optional amount of ENB derived units; d) a balance of propylene derived units; e) a branching index of greater than 0.5, preferably greater than 0.7; and f) a Mooney viscosity of from 15 ML to 100 MST. Articles made from such polymers are also described.